In the production of silicon-based fibers and other electronic components it is convenient to use the well-known chemical-vapor-deposition (CVD) process; see, for example, commonly owned U.S. Pat. Nos. 4,389,230 and 4,414,164. Thus, silicon can be obtained from one of the following reactions performed in a high-temperature furnace: EQU SiHCl.sub.3 +H.sub.2 .fwdarw.Si+3HCl (1) EQU SiCl.sub.4 +2H.sub.2 .fwdarw.Si+4HCl (2)
Its oxide, i.e. silica, is available from the reaction EQU SiCl.sub.4 +O.sub.2 .fwdarw.SiO.sub.2 +2Cl.sub.2 ( 3)
Zinc sulfide and zinc selenide, usable in fiber-optical technology for infrared transmissivity, are available in accordance with reactions EQU Zn+H.sub.2 S.fwdarw.ZnS+H.sub.2 ( 4) EQU Zn+H.sub.2 Se.fwdarw.ZnSe+H.sub.2 ( 5)
The CVD process is designed to minimize the problems of radiation absorption, e.g. intrinsically by substrate/impurity bonds and extrinsically through scattering by the presence of anomalous domains. These latter may result from grain dislocations in a crystalline substrate or, with a vitreous substrate, from crystalline zones or from separation of phases of different densities.
However, the aforedescribed redox reactions used in conventional CVD processes are sometimes accompanied by side reactions, involving different valence states, that give rise to undesired and often detrimental products. Reaction (4), for instance, may result in the formation of ZnH groups in the ZnS matrix, with the zinc in its monovalent form. These groups present absorption bands within the infrared range of interest lying between 2 and 12.mu..